As produced at the wellhead, crude petroleum oils contain substantial quantities of inorganic particulates and water and it has long been standard practice to require that the combined solids and water (BS&W) content be reduced to a value not exceeding a stated small percentage before the crude is introduced to a pipeline or supplied to a refinery. Such reduction of the BS&W content is necessary both to minimize damage to pipeline and refinery equipment from, e.g., corrosion and abrasive wear, and to minimize economic loss arising from transporting and processing the non-petroleum constituents making up the BS&W content. Though specifications vary among localities and refineries, a typical specification requires that the BS&W content of the crude not exceed 0.5% by volume.
The BS&W content of many crudes can be brought within pipeline specifications by adding chemical treating agents (commonly referred to in the field as demulsifiers) intended to break the very stable water-in-oil emulsions (including those which are complex) which characterize such crudes, and then recovering clean oil by gravitational separation, typically carried out in a conventional heater-treater. Other crudes, particularly the heavy oil crudes as a class and within that class especially the crudes obtained by enhanced production procedures, especially by thermal recovery procedures such as fireflooding and steamflooding, do not respond adequately to conventional treatment, and no fully satisfactory way has heretofore been devised for bringing the BS&W content of such crudes within pipeline specifications. The more difficultly treatable crudes are high viscous, so that in all events the raw crude from the wellhead must be diluted with a compatible hydrocarbon diluent, typically a wide gasoline fraction (condensate), to achieve adequate fluidity for handling and treatment. However, even when the more difficultly treatable crudes are thus diluted and then treated with one or more conventional demulsifiers, attempts to recover clean oil with a BS&W content within pipeline specifications by simple gravitational separation procedures do not usually succeed. Thus, for example, such attempts with heavy oil crudes obtained by fireflooding in the Husky Aberfeldy field have heretofore not succeeded in satisfactory removal of water and solids even though substantially all demulsifiers available from the oilfield service trade were tested.
Any successful treatment for separating particulate solids and water from the difficultly treatable heavy oil crudes requires that the water-in-oil emulsion characterizing such crudes first be at least destabilized, and that task has itself been difficult to accomplish. As described in detail in aforementioned application Ser. No. 397,935, it has been discovered that the emulsions of such crudes can be destabilized by uniformly distributing through the crude, while the crude is at a pH of at least 8 and advantageously at least 10, an agent capable of acting on the inorganic sulfur content of the crude, ammonium bisulfite being particularly useful as such an agent, the crude thus treated then being heated at 52.degree.-88.degree. C. (125.degree.-190.degree. F.) for at least a few minutes. Using that method, even the more difficult crudes, such as the fireflood crudes from the Husky Aberfeldy field, can be brought to a BS&W content below 0.5% by volume. During development of that method, it was discovered that breaking of the emulsions in the difficultly treatable crudes frequently produces a significant flocculated phase, occurring between the clean oil phase and the water phase upon phase separation, and that occurrence of the intermediate flocculated phase not only increases the time required for phase separation but also reduces the clean oil yield. Similar problems are encountered with the less difficultly treatable crudes when the emulsion of the crude is broken by other methods. There has thus been a need to provide a method for achieving a quicker and more effective phase separation during removal of particulate solids and water from petroleum crudes.